Neutron : Routed Provider Networks (no subnets declared in compute placement API: consequences?)

Hi neutron experts

Have a cloud built with multiple network segments (RPN) . (kolla-ansible, openstack ussuri), things are running OK (on the network level):

networks have DHCP agents ok (*os network agent list --agent-type dhcp --network $networkID* )

all network segments are listed in Host Aggregates

BUT if I run through all the existing segments , NONE have a (compute service) inventory declared for each segment IPv4 subnet i.e *os resource provider inventory list $segmentID * returns no output. (official doc on RPN says this should exist)

What feature may not function if this inventory is missing ?

I don't quite understand what role this IPv4 subnet compute service inventory plays here (during placement? port declaration ?)

thanks Andrew